Shortly after the Leipzig L-IV atomic pile — worked on by Werner Heisenberg and Robert Doepel — demonstrated Germany's first signs of neutron propagation, the device was checked for a possible heavy water leak. During the inspection, air leaked in, igniting the uranium powder inside. The burning uranium boiled the water jacket, generating enough steam pressure to blow the reactor apart. Burning uranium powder scattered throughout the lab causing a larger fire at the facility.[1][2]

While demonstrating his technique to visiting scientists at Los Alamos, Canadian physicistLouis Slotin manually assembled a critical mass of plutonium. A momentary slip of a screwdriver caused a prompt critical reaction. Slotin died on May 30 from massive radiation poisoning, with an estimated dose of 1,000 rads (rad), or 10 grays (Gy). Seven observers, who received doses as high as 166 rads, survived, yet three died within a few decades from conditions believed to be radiation-related.[4]

In the above incidents, both Daghlian (August 21, 1945 case) and Slotin (May 21, 1946 case), were working with the same bomb core which became known as the "demon core", which was eventually utilized for the Able test detonation on July 1, 1946.

A USAF B-36 bomber, AF Ser. No. 44-92075, was flying a simulated combat mission from Eielson Air Force Base, near Fairbanks, Alaska, to Carswell Air Force Base in Fort Worth, Texas, carrying one weapon containing a dummy warhead. The warhead contained uranium instead of plutonium. After six hours of flight, the bomber experienced mechanical problems and was forced to shut down three of its six engines at an altitude of 12,000 feet (3,700 m). Fearing that severe weather and icing would jeopardize a safe emergency landing, the weapon was jettisoned over the Pacific Ocean from a height of 8,000 ft (2,400 m). The weapon's high explosives detonated upon impact with a bright flash visible. All of the sixteen crew members and one passenger were able to parachute from the plane and twelve were subsequently rescued from Princess Royal Island. The Pentagon's summary report does not mention if the weapon was later recovered.[5]

Three minutes after departure from Kirtland Air Force Base in Albuquerque a USAF B-29 bomber carrying a nuclear weapon, four spare detonators, and a crew of thirteen crashed into a mountain near Manzano Base. The crash resulted in a fire which the New York Times reported as being visible from 15 miles (24 km). The bomb's casing was completely demolished and its high explosives ignited upon contact with the plane's burning fuel. However, according to the Department of Defense, the four spare detonators and all nuclear components were recovered. A nuclear detonation was not possible because, while on board, the weapon's core was not in the weapon for safety reasons. All thirteen crew members died.[5]

A USAF B-29 bomber with a Mark 4 nuclear bomb on board, flying to Guam at the request of General Douglas MacArthur, experienced malfunctions with runaway propellers and landing gear retraction during take-off and crashed while attempting an emergency landing. In the resulting fire, the bomb's high explosive material exploded, killing nineteen people from the crew and rescue personnel. Brigadier General Robert F. Travis was among the dead.[7]

During the Castle Bravo test of the first deployable hydrogen bomb, a miscalculation resulted in the explosion being over twice as large as predicted, with a total explosive force of 15 megatons of TNT (63 PJ). Of the total yield, 10 Mt (42 PJ) were from fission of the natural uranium tamper, but those fission reactions were quite dirty, producing a large amount of fallout. Combined with the much larger than expected yield and an unanticipated wind shift radioactive fallout was spread eastward onto the inhabited Rongelap and Rongerik Atolls. These islands were not evacuated before the explosion due to the financial cost involved, but many of the Marshall Islands natives have since suffered from radiation burns and radioactive dusting and also similar fates as the Japanese fishermen and have received little, if any, compensation from the federal government[citation needed]. A Japanese fishing boat, the Daigo Fukuryu Maru/Lucky Dragon, also came into contact with the fallout, which caused many of the crew to become ill, with one fatality. The test resulted in an international uproar and reignited Japanese concerns about radiation, especially with regard to the possible contamination of fish. Personal accounts of the Rongelap people can be seen in the documentary Children of Armageddon.

Operator error led to a partial core meltdown in the experimental EBR-Ibreeder reactor, resulting in temporarily elevated radioactivity levels in the reactor building and necessitating significant repair.[9][10]

A USAF B-47 Stratojet, AF Ser. No. 52-534, on a non-stop mission from MacDill Air Force Base, Florida, to an overseas base descended into a cloud formation at 14,000 feet over the Mediterranean in preparation for an in-air refuelling and vanished while carrying two nuclear weapon cores. The plane was lost while flying through dense clouds, and the cores and other wreckage were never located.[11][12][13]

A USAF B-47 crashed into a storage igloo spreading burning fuel over three Mark 6 nuclear bombs at RAF Lakenheath. A bomb disposal expert stated it was a miracle exposed detonators on one bomb did not fire, which presumably would have released nuclear material into the environment.[14]

A B-36 ferrying a nuclear weapon from Biggs AFB to Kirtland AFB dropped a nuclear weapon on approach to Kirtland AFB. The weapon struck the ground 4.5 miles south of the Kirtland control tower and 0.3 miles west of the Sandia Base reservation. The weapon was completely destroyed by the detonation of its high explosive material, creating a crater 12 feet deep and 25 feet in diameter. Radioactive contamination at the crater lip amounted to 0.5 milliroentgen.[13]

July 28, 1957 – Atlantic Ocean – Two weapons jettisoned and not recovered

A USAF C-124 aircraft from Dover Air Force Base, Delaware was carrying three nuclear bombs over the Atlantic Ocean when it experienced a loss of power. For their own safety, the crew jettisoned two nuclear bombs, which were never recovered.[6]

A fire began in a theoretically fireproof area inside the plutonium processing building, in a materials handling glove box and spread through the ventilation system into the stack filters at the Rocky Flats weapons mill 27 kilometres (17 mi) from Denver, Colorado. The fire quickly spread to the plutonium as various safety features failed. As the containment ability of the facility became compromised, plumes of radioactive smoke were sent high into the air. The fire raged inside the building for 13 hours over the night of the 11th & 12th before firefighters could finally extinguish it. In the aftermath, Department of Energy officials, and the Dow Chemical officials who ran the facility, did not admit the extent of the catastrophe, or the radiation danger, to local officials or the media. Knowledge of the extent of the damage and contamination was kept from the public for years. After the fire, plutonium was detected 30 miles from the plant - heavily contaminating the region, including a school 12 miles away, as well as including Denver and its environs. An independent group of scientists conducting off-site testing 13 years later found plutonium contamination in areas in nearby Rocky Flats to be 400 to 1,500 times higher than normal, higher than any ever recorded near any urban area, including Nagasaki. The Atomic Energy Commission then conducted its own off-site study, and that study confirmed plutonium contamination as far as thirty miles from the plant.[15][16][17][18]

See Kyshtym disaster. A cooling system failure at the Mayak nuclear processing plant resulted in a major explosion and release of radioactive materials. A large area was subjected to radioactive contamination and thousands of local inhabitants were evacuated.[19]

See Windscale fire. Technicians mistakenly overheated Windscale Pile No. 1 during an annealing process to release Wigner energy from graphite portions of the reactor. Poorly placed temperature sensors indicated the reactor was cooling rather than heating. The excess heat led to the failure of a nuclear cartridge, which in turn allowed uranium and irradiated graphite to react with air. The resulting fire burned for days, damaging a significant portion of the reactor core. About 150 burning fuel cells could not be lifted from the core, but operators succeeded in creating a firebreak by removing nearby fuel cells. An effort to cool the graphite core with water eventually quenched the fire. The reactor had released radioactive gases into the surrounding countryside, primarily in the form of iodine-131 (131I). Milk distribution was banned in a 200-square-mile (520 km2) area around the reactor for several weeks. A 1987 report by the National Radiological Protection Board predicted the accident would cause as many as 33 long-term cancer deaths, although the Medical Research Council Committee concluded that "it is in the highest degree unlikely that any harm has been done to the health of anybody, whether a worker in the Windscale plant or a member of the general public." The reactor that burned was one of two air-cooled, graphite-moderated natural uranium reactors at the site used for production of plutonium.[20][21][22]

During a simulated takeoff, a wheel casting failure caused the tail of a USAF B-47 carrying an armed nuclear weapon to hit the runway, rupturing a fuel tank and sparking a fire. Some contamination was detected immediately following the accident.[24][25]

A USAF B-47E bomber, number 53-1876A, was flying from Hunter Air Force Base in Savannah, Georgia, to England in a formation of four B-47s on a top-secret mission called Operation Snow Flurry to perform a mock bombing exercise. The flight navigator/bombardier climbed on 10 feet (3 m) long 7,600 pounds (3,447 kg) 30 kiloton Mark 6 nuclear bomb to check the locking harness. He accidentally pushed the emergency release lever, the bomb hit the bomb-bay doors, forced its way out and went into 15,000 feet (4,572 m) free fall. The high explosive detonator went off after it hit the ground 6 ½ miles east of Florence, South Carolina, in Mars Bluff, creating a 70 feet (21 m) wide crater, 30 feet (9 m) deep.[27] A nearby house was destroyed and several people were injured.[28]

A supercritical portion of highly enriched uranyl nitrate was allowed to collect in the drum causing a prompt neutron criticality in the C-1 wing of building 9212 at the Oak Ridge National LaboratoryY-12 complex. It is estimated that the reaction produced 1.3 × 1018 fissions. Eight employees were in close proximity to the drum during the accident, receiving neutron doses ranging from 30 to 477 rems. No fatalities were reported.[29]

A USAF B-47 bomber developed a fire shortly after take-off and went down with a nuclear weapon on board from an altitude of 1,500 ft (460 m). The detonation of the high explosive material in the bomb created a crater 6 feet deep and 35 feet in diameter. Three crew members escaped, and one was killed.[30]

A USAF B-47 bomber with a nuclear weapon on board developed a fire while on the ground. The aircraft wreckage and the site of the accident were contaminated after a limited explosion of non-nuclear material.[31]

A grounded USAF F-100C Super Sabre supersonic fighter-bomber with a nuclear weapon loaded developed a fire on one of the USAF Pacific bases after its external fuel tanks were dropped and exploded during a practice alert. The resulting fire was put out in seven minutes and there was no nuclear weapon explosion.[32]

A USAF C-124 transporting two nuclear weapons without fissile cores crashed and burned down during take-off. The high explosive detonators did not go off. The wreckage area experienced limited contamination.[33]

A USAF B-52F-100-BO, number 57-036, with two nuclear weapons collided at 32,000 feet (9,754 m) with a KC-135 refueling aircraft, number 57-1513, during a refueling procedure near Hardinsburg, Kentucky. The planes took off from Columbus Air Force Base in Mississippi. After collision, both planes crashed killing eight crew members. One unarmed nuclear weapon was partially damaged, but no contamination resulted.[35]

A chemical explosion occurred during decontamination of processing machinery in the radiochemical processing plant at Oak Ridge National Laboratory in Tennessee . (Report ORNL-2989, Oak Ridge National Laboratory). The accident resulted in the release of about 15 grams (0.53 oz) of 239Pu.

A leak developed in the steam generators and in a pipe leading to the compensator reception on the ill-fated K-8 while the SovietNorthern FleetNovember-classsubmarine was on exercise. While the crew rigged an improvised cooling system, radioactive gases leaked into the vessel and three of the crew suffered visible radiation injuries according to radiological experts in Moscow. Some crew members had been exposed to doses of up to 1.8–2 Sv (180–200 rem).[37]

During a maintenance shutdown, the SL-1 experimental nuclear reactor underwent a prompt critical reaction causing core materials to explosively vaporize. Water hammer estimated at 10,000 pounds per square inch (69,000 kPa) struck the top of the reactor vessel propelling the entire reactor vessel upwards over 9 feet (2.7 m) in the air. One operator who had been standing on top of the vessel was killed when a shield plug impaled him and lodged in the ceiling. Two other military personnel were also killed from the trauma of the explosion, one of which had removed the central control rod too far. The plant had to be dismantled and the contamination was buried permanently nearby. Most of the release of radioactive materials was concentrated within the reactor building.

A USAF B-52bomber caught fire and exploded in midair due to a major leak in a wing fuel cell 12 miles (19 km) north of Seymour Johnson Air Force Base, North Carolina. Five crewmen parachuted to safety, but three died—two in the aircraft and one on landing. The incident released the bomber's two Mark 39hydrogen bombs. Three of the four arming devices on one of the bombs activated, causing it to carry out many of the steps needed to arm itself, such as the charging of the firing capacitors and, critically, the deployment of a 100-foot (30 m) diameter retardation parachute. The parachute allowed the bomb to hit the ground with little damage. The fourth arming device — the pilot's safe/arm switch — was not activated preventing detonation. The second bomb plunged into a muddy field at around 700 mph (300 m/s) and disintegrated. Its tail was discovered about 20 feet (6 m) down and much of the bomb recovered, including the tritium bottle and the plutonium. However, excavation was abandoned due to uncontrollable ground water flooding. Most of the thermonuclear stage, containing uranium, was left on site. It is estimated to lie around 55 feet (17 m) below ground. The Air Force purchased the land and fenced it off to prevent its disturbance, and it is tested regularly for contamination, although none has so far been found.[38]

The SovietHotel-class submarine K-19 suffered a failure in its cooling system. Reactor core temperatures reached 800 °C (1,500 °F), nearly enough to melt the fuel rods, although the crew was able to regain temperature control by using emergency procedures. The incident contaminated parts of the ship, some of the onboard ballistic missiles and the crew, resulting in several fatalities. The movie K-19: The Widowmaker, starring Harrison Ford and Liam Neeson, offers a controversially fictionalized story of these events.

The second French underground nuclear test, codenamed Béryl, took place in a shaft under mount Taourirt, near In Ecker, 150 km (100 mi) north of Tamanrasset, AlgerianSahara. Due to improper sealing of the shaft, a spectacular flame burst through the concrete cap and radioactive gases and dust were vented into the atmosphere. The plume climbed up to 2600 m (8500 ft) high and radiation was detected hundreds of km away. About a hundred soldiers and officials, including two ministers, were irradiated. The number of contaminated Algerians is unknown.

April 10, 1963 – Loss of nuclear reactor

Submarine USS Thresher sinks about 190 nmi (220 mi; 350 km) east of Cape Cod, Massachusetts due to improper welds allowing in seawater which forced a shutdown of the reactor. Poor design of its emergency ballast system prevented the ship from surfacing and the disabled ship ultimately descended to crush depth and imploded.

A USAF B-52 on airborne alert duty encountered a severe winter storm and extreme turbulence, ultimately disintegrating in mid-air over South Central Pennsylvania.[39] Only the two pilots survived. One crew member failed to bail out and the rest succumbed to injuries or exposure to the harsh winter weather. A search for the missing weapons was initiated, and recovery was effected from portions of the wreckage at a farm northwest of Frostburg, MD.

February 1965 – Lenin a Soviet nuclear icebreaker, suffered a loss-of-coolant accident. After being shut down for refueling, the coolant was removed from the number two reactor before the spent fuel had been removed. As a result, some of the fuel elements melted and deformed inside the reactor. This was discovered when the spent elements were being unloaded for storage and disposal. 124 fuel assemblies (about 60% of the total) were stuck in the reactor core. It was decided to remove the fuel, control grid, and control rods as a unit for disposal; they were placed in a special cask, solidified, stored for two years, and dumped in Tsivolki Bay (near the Novaya Zemlya archipelago) in 1967.

A USAF B-52 carrying four hydrogen bombs collided with a USAFKC-135jet tanker during over-ocean in-flight refueling. Four of the B-52's seven crew members parachuted to safety while the remaining three were killed along with all four of the KC-135's crew. The conventional explosives in two of the bombs detonated upon impact with the ground, dispersing plutonium over nearby farms. A third bomb landed intact near Palomares while the fourth fell 12 miles (19 km) off the coast into the Mediterranean sea. The U.S. Navy conducted a three-month search involving 12,000 men and successfully recovered the fourth bomb. The U.S. Navy employed the use of the deep-diving research submarine DSV Alvin to aid in the recovery efforts. During the ensuing cleanup, 1,500 tonnes (1,700 short tons) of radioactive soil and tomato plants were shipped to a nuclear dump in Aiken, South Carolina. The U.S. settled claims by 522 Palomares residents for $600,000. The town also received a $200,000 desalinization plant. The motion picture Men of Honor (2000), starring Cuba Gooding, Jr., as USN Diver, Master Chief Petty Officer Carl Brashear, and Robert De Niro as USN Diver, Chief Petty Officer Billy Sunday, contained an account of the fourth bomb's recovery.[42]

1967 – Lenin a Soviet nuclear icebreaker, suffered a second accident; a cooling system leak which occurred in 1967, shortly after refueling. Finding the leak required breaking through the concrete and metal biological shield with sledgehammers. Once the leak was found, it became apparent that the sledgehammer damage could not be repaired; subsequently, all three reactors were removed, and replaced by two OK-900 reactors, by early 1970.[43]

A fire broke out in the navigator's compartment of a USAF B-52 near Thule Air Base, Greenland. The bomber crashed 7 miles (11 km) from the air base, rupturing its nuclear payload of four hydrogen bombs. The recovery and decontamination effort was complicated by Greenland's harsh weather. Contaminated ice and debris were buried in the United States. Bomb fragments were recycled by Pantex, in Amarillo, Texas. The incident caused outrage and protests in Denmark, as Greenland is a Danish possession and Denmark forbade nuclear weapons on its territory.

The USS Scorpion (SSN-589) sank while en route from Rota, Spain, to Norfolk, Virginia, USA. The cause of sinking remains unknown; all 99 officers and men on board were killed. The wreckage of the ship, its S5W reactor, and its two Mark 45 torpedoes with W34 nuclear warheads, remain on the sea floor in more than 3,000 m (9,800 ft) of water.

During sea trials the Soviet nuclear submarine K-27 (Project 645) suffered severe problems with its reactor cooling systems. After spending some time at reduced power, reactor output inexplicably dropped and sensors detected an increase of gamma radiation in the reactor compartment to 150 rad/h. The safety buffer tank released radioactive gases further contaminating the submarine. The crew shut the reactor down and subsequent investigation found that approximately 20% of the fuel assemblies were damaged. The entire submarine was scuttled in the Kara Sea in 1981.

While in the naval yards at Severodvinsk for repairs Soviet Yankee-classnuclear submarine K-140 suffered an uncontrolled increase of the reactor's power output. One of the reactors activated automatically when workers raised control rods to a higher position and power increased to 18 times normal, while pressure and temperature levels in the reactor increased to four times normal. The accident also increased radiation levels aboard the vessel. The problem was traced to the incorrect installation of control rod electrical cables.

An accident in which 5 kilograms of plutonium burnt inside a glovebox at Rocky Flats. Cleanup took two years and was the costliest industrial accident ever to occur in the United States at that time.[44][45][46]

In Area 8 on Yucca Flat, the 10 kiloton "Baneberry" weapons test of Operation Emery detonated as planned at the bottom of a sealed vertical shaft 900 feet below the Earth's surface but the device's energy cracked the soil in unexpected ways, causing a fissure near ground zero and the failure of the shaft stemming and cap.[48] A plume of hot gases and radioactive dust was released three and a half minutes after ignition,[49] and continuing for many hours, raining fallout on workers within NTS. Six percent of the explosion's radioactive products were vented. The plume released 6.7 MCi of radioactive material, including 80 kCi of Iodine-131 and a high ratio of noble gases.[50] After dropping a portion of its load in the area, the hot cloud's lighter particles were carried to three altitudes and conveyed by winter storms and the jet stream to be deposited heavily as radionuclide-laden snow in Lassen and Sierra counties in northeast California, and to lesser degrees in northern Nevada, southern Idaho and some eastern sections of Oregon and Washington states.[51] The three diverging jet stream layers conducted radionuclides across the US to Canada, the Gulf of Mexico and the Atlantic Ocean. Some 86 workers at the site were exposed to radioactivity, but according to the Department of Energy none received a dose exceeding site guidelines and, similarly, radiation drifting offsite was not considered to pose a hazard by the DOE.[52] In March 2009, TIME magazine identified the Baneberry Test as one of the world's worst nuclear disasters.[53]

A major fire and two explosions contaminated the plant and grounds of a plutonium fabrication facility resulting in a permanent shutdown.

1975 – location unknown – Contamination

Radioactive resin contaminates the AmericanSturgeon-class submarineUSS Guardfish after wind unexpectedly blows the powder back towards the ship. The resin is used to remove dissolved radioactive minerals and particles from the primary coolant loops of submarines. This type of accident was fairly common; however, U.S. Navy nuclear vessels no longer discharge resin at sea.

An explosion at the Hanford site Plutonium Finishing Plant blew out a quarter-inch-thick lead glass window. Harold McCluskey, a worker, was showered with nitric acid and radioactive glass. He inhaled the largest dose of 241Am ever recorded, about 500 times the U.S. government occupational standards. The worker was placed in isolation for five months and given an experimental drug to flush the isotope from his body. By 1977, his body's radiation count had fallen by about 80 percent. He died of natural causes in 1987 at age 75.[54]

Cosmos 954, a SovietRadar Ocean Reconnaissance Satellite with an onboard nuclear reactor, failed to separate from its booster and broke up on reentry over Canada. The fuel was spread over a wide area and some radioactive pieces were recovered. The Soviet Union eventually paid the Canadian Government $3 million CAD for expenses relating to the crash.

September 18, 1980 – At about 6:30 p.m., an airman conducting maintenance on a USAF Titan-II missile at Little Rock Air Force Base's Launch Complex 374-7 in Southside (Van Buren County), just north of Damascus, Arkansas, dropped a socket from a socket wrench, which fell about 80 feet (24 m) before hitting and piercing the skin on the rocket's first-stage fuel tank, causing it to leak. The area was evacuated. At about 3:00 a.m., on September 19, 1980, the hypergolic fuel exploded. The W53 warhead landed about 100 feet (30 m) from the launch complex's entry gate; its safety features operated correctly and prevented any loss of radioactive material. An Air Force airman was killed and the launch complex was destroyed.[56]

August 8, 1982 – While on duty in the Barents Sea, there was a release of liquid metal coolant from the reactor of the Soviet Project 705 Alfa-class submarineK-123. The accident was caused by a leak in the steam generator. Approximately two tons of metal alloy leaked into the reactor compartment, irreparably damaging the reactor such that it had to be replaced. It took nine years to repair the submarine.

January 3, 1983 – The Soviet nuclear-powered spy satellite Kosmos 1402 burns up over the South Atlantic.

1986 – The U.S. government declassifies 19,000 pages of documents indicating that between 1946 and 1986, the Hanford Site near Richland, Washington, released thousands of US gallons of radioactive liquids. Many of the people living in the affected area received low doses of radiation from 131I.

October 3, 1986 – 480 miles (770 km) east of Bermuda, the SovietYankee-I-classsubmarineK-219 experienced an explosion in one of its missile tubes and at least three crew members were killed. Sixteen nuclear missiles and two reactors were on board. Soviet leaderMikhail Gorbachev privately communicated news of the disaster to U.S. PresidentRonald Reagan before publicly acknowledging the incident on October 4. Two days later, on October 6, the submarine sank in the Atlantic Ocean while under tow in 18,000 feet (5,500 m) of water.[58]

October 1988 – At the nuclear trigger assembly facility at Rocky Flats in Colorado, two employees and a D.O.E. inspector inhaled radioactive particles, causing closure of the plant. Several safety violations were cited, including uncalibrated monitors, inadequate fire equipment, and groundwater contaminated with radioactivity.

1997 – Georgian soldiers suffer radiation poisoning and burns. They are eventually traced back to training sources abandoned, forgotten, and unlabeled after the dissolution of the Soviet Union. One was a 137Cs pellet in a pocket of a shared jacket which put out about 130,000 times the level of background radiation at 1 meter distance.[59]

February 2003: Oak Ridge, TennesseeY-12 facility. During the final testing of a new saltless uranium processing method, there was a small explosion followed by a fire. The explosion occurred in an unvented vessel containing unreacted calcium, water and depleted uranium. An exothermic reaction in the vessel generated enough steam to burst the container. This small explosion breached its glovebox, allowing air to enter and ignite some loose uranium powder. Three employees were contaminated. BWXT Y-12 (now B&W Y-12), a partnership of Babcock & Wilcox and Bechtel, was fined $82,500 for the accident.[60]

(French) Jean-Hugues Oppel, Réveillez le président !, Éditions Payot et rivages, 2007 (ISBN 978-2-7436-1630-4). The book is a fiction about the nuclear weapons of France; the book also contains about ten chapters on true historical incidents involving nuclear weapons and strategy (during the second half of the twentieth century).